This disclosure relates generally to the recovery or distillation of fresh water from salt water. While many previous arrangements have been proposed and used to distill salt water for desalinization purposes, these typically require direct processing of seawater or salt water, which is treated in a heat exchanger in conjunction with a condensing surface for collecting the evaporated fresh water. The residual brine or salt deposits must then be returned to the sea or otherwise disposed of.
The present method utilizes an underground natural geological structure as a "reactor vessel" in which vaporization occurs. The necessity ofhandling salt water as a vapor source, and of handling brine is completely eliminated and only water vapor enters the mechanical apparatus for condensing fresh water. By combining natural underground containment of salt water and a large supply of water vapor, the present method makes practical the recovery of fresh water on a large scale.
It is recognized that solar stills such as shown in U.S. Pat. Nos. 3,138,546 and 3,468,762 utilize the general concept of evaporating seawater within a chamber and drawing off the vapor for condensation recovery. However, these prior disclosures described such processes utilizing only manmade vessels and therefore must also involve the handling of the resulting waste products. U.S. Pat. No. 2,716,446 describes evaporation of water in a manmade container by reduction of pressure. U.S. Pat. No. 3,283,813 describes salt water conversion in a sub-surface chamber, using an osmosis process.
The present invention makes use of thenatural containment of salt water or seawater available in areas adjacent to a sea coast, where salt water is occasionally found in an underground chamber capped by an impervious cover layer, and more commonly where salt water is found in sand and gravel filled water permeable strata capped by impervious cover layers and forming with appropriate "closure" what are commonly called in the petroleum industry, domelike, anticlinal, monoclinal, and similar "structures;" which "structures" are sought as potential traps for petroleum and natural gas if there is also present a petroleum source rock and a water "drive."
The underground body of water should be sufficiently large so that its area and the effective rate of evaporation is virtually unaffected by any local channels having an increased concentration of salt in solution being carried down structure to sea water dispersal or deep disposal; and said underground body of water should have offshore communication with a body of seawater to permit replenishing with salt water the discharged cooler, more dense waste brine as the brine sinks and travels upon and along impermeable shale stratum 19, FIG. 1, which stratum is shown dipping largely seaward. (The temperature and brine density result from evaporational effects accomplished by appropriate placement of the family of vapor outlet pipes represented by 15, FIG. 1). The dense discharged brine would tend to be simultaneously replaced by the less saline, less dense, warmer seawater, along the highest points of seawater access to the stratum 12; especially along directions and through the higher channels in the gravel zones not being used for the discharge of the heavier brines tending to seek the lowest level of hydraulic access to the sea.
Nearness to the sea would frequently allow the low cost use of seawater to cool the condensing equipment and by injecting to the underground structure the warm discharge water from the condensers, both the heat of condensation can be recovered usefully, and the injected seawater may also replace the fresh water produced and the brine discharged from the structure.
The method eliminates direct handling or manipulation of salt brine or salt deposits; and the moderate temperatures, pressures, and conditions of operation used by the method generally avoid many problems that beset other desalinization or distillation systems such as, the corrosion of equipment, the accumulation of saline residues, and the relatively expensive maintenance of equipment operating at higher temperatures or abnormal pressures.
The gravel exposures along the offshore ocean bottom generally would form wise, three dimensional, undersea brine dispersal zones for the natural redilution of the waste brines. Ecologically these redilution zones may be selected and managed so as to compare favorably with many natural redilution process taking place in coastal bays where increased salinity results from evaporation, as well as to compare favorably with many man managed systems that seek to protect the shoreline environment from excessive saline accumulations.
Appropriate structures for the application of the invention may be selected from the wide variety of non-productive structures already mapped by the petroleum industry, and from the maps of structural geology published by various governmental professional and educational entities.